LMR14030-Q1: No output when touch the divider resistors of the FB pin

Sherry Liang

Part Number: LMR14030-Q1

Dear team,

When the customer touches the voltage divider resistors of the FB pin using their hands, there will be no output. Could you please help tell me the reason and solve this problem?

Thanks & Best Regards,

Sherry

over 6 years ago

0 Jason Wang (BSR-MV) over 6 years ago

TI__Genius 9550 points

Sherry,
FB pin is high resistance, when you touch the divider resistor, you must touch the traces which connect to the FB pin. You can't touch the divider resistor as request.

0 Andy Chen over 6 years ago

TI__Mastermind 34165 points

Hi Sherry,

One possible solution is to use low resistance FB divider if customer has such testing requirement, for example the bottom side resistor can be 100ohm--1Kohm, then calculate high side resistor for target output voltage. the draw back is little higher bias current on output.

0 Sherry Liang over 6 years ago in reply to Andy Chen

TI__Genius 10255 points

Hi Andy,

My customer adds a capacitor at the FB pin, which reduces the number of failures(no output). Is this solution feasible? If so, how much capacitor value do you recommend? And is there any drawback about this solution? If not, could you please help tell me the reasons?

Thanks & Best Regards,
Sherry

0 Andy Chen over 6 years ago in reply to Sherry Liang

TI__Mastermind 34165 points

Hi Sherry,

Adding capacitor on FB pin has big impact on control loop stability, some times we need to add capacitor on FB pin to GND if electrolytic capacitor with high ESR is used. pls send application circuit to me at andy.chen@ti.com for double check.

0 Sherry Liang over 6 years ago in reply to Andy Chen

TI__Genius 10255 points

Hi Andy,

Thanks for your explanation. I will send you the circuit when I got it from my customer.

Thanks & Best Regards,
Sherry

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LMR14030-Q1: No output when touch the divider resistors of the FB pin